Communication systems employ Code Division Multiple Access ("CDMA") modulation techniques to permit a large number of system users to communicate with one another. In typical CDMA systems, communication is achieved by using spreading sequences for each channel that modulate the information bits to be transmitted between two communication units, for example between base stations and mobile stations. This results in a plurality of transmitted signals sharing the same frequency. The ability of such a system to work is based on the fact that each signal is time and/or frequency coded with a spreading sequence, such as with a pseudo-random noise ("PN") sequence, to permit signal separation and reconstruction at the receiver. Particular transmitted signals are retrieved from the communication channel by despreading a signal from all of the signals by using a known user despreading sequence related to the spreading sequence implemented at the transmitter.
The geographic coverage provided by the communication system is divided into coverage cells, where each cell corresponds to a base station. The cell is then further divided for certain types of base stations into multiple sectors, where each sector uses multiple carrier channels to transmit the voice or data bits to other communication units. One of many cell resource management problems that the base station must consider is how to manage forward link power utilization. The base station must determine how much power is being transmitted, such that the maximum power output of the base station amplifiers is not exceeded when additional power is requested. For example, when calls are added to a base station that employs no forward link power overload control, the power requests are accepted until the amplifier runs out of headroom, potentially reaching an overload condition. This overload condition can damage the base station and clip the transmitted signal, degrading the call quality.
In conventional CDMA systems that have some form of power control, only the highest levels of system management know the forward link power conditions. As a consequence, the feedback response is very slow between a base station's controller and the rest of the base station. There is no way the base station can quickly detect when forward link power utilization is approaching the limit of the sector power so as to protect the amplifier and to maintain existing call quality. Conventional base stations can reach maximum power without the base station control system realizing that an overload condition has occurred. These drawbacks of conventional base stations have required an over-design of the amplifiers to cope with the overload conditions. Extra margin on the amplifier translates into more expensive and larger systems without a guarantee that the base station will perform without the overloads.